Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.64   11.385%   $170.0181   $170.02   $170.00   $170.00  
  Purchase #2 $86.73   13.518%   $98.4542   $98.45   $98.45   $98.50  
  Purchase #3 $135.28   9.841%   $148.5929   $148.59   $148.60   $148.60  
  Purchase #4 $233.81   8.122%   $252.8   $252.80   $252.80   $252.80  
  Purchase #5 $11.87   7.586%   $12.7705   $12.77   $12.75   $12.80  
  Purchase #6 $95.97   9.748%   $105.3252   $105.33   $105.35   $105.30  
  Purchase #7 $156.87   6.104%   $166.4453   $166.45   $166.45   $166.40  
  7 purchase totals = $873.17       $954.4062   $954.41   $954.40   $954.40